Raman spectra and XPS studies of phase changes in Ge ₂ Sb ₂ Te ₅ films

Ge2Sb2Te5 film was deposited by RF magnetron sputtering on Si (100) substrate. The structure of amorphous and crystalline Ge2Sb2Te5 thin films was investigated using XRD, Raman spectra and XPS. XRD measurements revealed the existence of two different crystalline phases, which has a FCC structure and a hexagonal structure, respectively. The broad peak in the Raman spectra of amorphous Ge2Sb2Te5 film is due to the amorphous –Te–Te– stretching. As the annealing temperature increases, the broad peak separates into two peaks, which indicates that the heteropolar bond in GeTe4 and the Sb–Sb bond are connected with four Te atoms and other units such as (TeSb) Sb–Sb (Te2) and (Sb2) Sb–Sb (Te2), where some of the four Te atoms in the above formula are replaced by Sb atoms, remain in crystalline Ge2Sb2Te5 thin film. And from the results of Raman spectra and XPS, higher the annealing temperature, more Te atoms bond to Ge atoms and more Sb atoms substitute Te in (Te2) Sb–Sb (Te2).